The invention relates to a transconductor.
FIG. 1 illustrates a known transconductor comprising a voltage input terminal Vin1, a current output terminal Iout1, a supply voltage terminal Vcc1, and two control voltage terminals Vreg1+ and Vreg1xe2x88x92. A control voltage is to be applied between the control voltage terminals Vreg1= and Vreg1xe2x88x92 to control the transconductance of the transconductor.
The voltage input terminal Vin1 is connected to the base of a transistor Q11, whose emitter is connected to a ground terminal via a resistor R11 and whose collector is connected to an interconnection point between emitters of two transistors Q12 and Q13. The base of the transistor Q12 is connected to the control voltage terminal Vreg1+, while the base of the transistor Q13 is connected to the control voltage terminal Vreg1xe2x88x92. The collector of the transistor Q12 is connected to the current output terminal Iout1, while the collector of the transistor Q13 is connected to the supply voltage terminal Vcc1.
By varying the voltage between the control voltage terminals Vreg1+ and Vreg1xe2x88x92, the output current on the current output terminal Iout1 will vary correspondingly.
The known transconductor shown in FIG. 1 cannot be used at low supply voltages applied between the supply voltage terminal Vcc1 and ground since it requires quite a large voltage range due to the fact that the transistors Q11, Q12 and Q13 are stacked on each other.
The object of the invention is to bring about a transconductor that enables power control also at low supply voltages.
This is attained in the transconductor according to the invention in that it comprises only two transistors without stacking.
Hereby, operation at a lower supply voltage is enabled.